Currently sshd tests for /etc/nologin *both* through the pam and on its own.
This is very annoying - one assumes that it's possible to override the tests by
modifying the /etc/pam.d/sshd, but then it turns out that the pam_nologin in
/etc/pam.d/sshd is redundant and that sshd does the testing itself and there is
no way to override it.
In short, this RFE is for:
1) Configuration option to override the /etc/nologin testing in sshd itself (see
also bug #47298).
2) Change in the default config shipped by RedHat to have the override turned on.
P.S. According to bug #54108, the pam_nologin needs to be moved from auth to
account in order to work properly even with the RSA authentication.

Without solving bug 54108 the nologin processing shouldn't be removed. Also
note, that the contents of /etc/nologin should be dumped on client's terminal.
This isn't/cannot be the case of using pam for nologin processing.
Adding a new configuration option is also not good without having it in upstream
portable OpenSSH first so please report it to http://bugzilla.mindrot.org/.